Fluid braking apparatus and compressor therefor



April 1936- w. F. OLIVER 2,038,055-

FLUID BRAK ING APPARATUS AND CQMPRESSQR THEREFOR at l M 47 Filed Dec.12, 1951 3, 74 I I j 1:?

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FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 1931 7Sheets-Sheet 2 April 21, 1936. w OLIVER 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 1951 7Sheets-Sheet 3 VMUZZMQZ LOLZZLJM, J5 2m WM April 21, 1936. w Q| |VE R2,038,055

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FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR Filed Dec. 12, 195.1. 7Sheets-Sheet 5 I FLUID BRAKING APPARATUS AND COMPRESSOR THEREFOR FiledDec. 12, 1931 '7 Sheets-Sheet 6 I mew/M, 2 w V /WL Aril 21, 19360 w. F.OLIVER 2,038,055

FLUID BRAKING APPARATUS AND COMPRESSOR, THEREFOR Filed Dec. 12, 1951 7Sheets-Sheet 7 22062275? 1 v h/a ZZacef0Za'r/e2" Patentedf Apr. 21, 1936UNITED STATES ,PATENT orrlca FLUID. BRAKING APPARATUS AND comassson'rnEaEron Wallace F..0liver, Detroit, Mich asaignor to Bydraulic BrakeCompany, Los Angeies, Galit, a corporation of CaIifornia ApplicationDecember 12, 1931, Serial No.'-580,5'l3

13 Claims. (01. Bil-54.6)

My invention is concerned with improvements in hydraulic brakingapparatus of the type in which a liquid is caused to flow to and frombraking positions in the setting and releasing of 5 brakes.

One object of my invention isan improved means of maintaining a constantamount of liquid in the system, compensating for volumetric losses bycontraction or leakage, and relieving any volumetric excess caused bythe replenishing means or by heat expansion. Maintaining a constantliquid volume for the system is desirable, for otherwise the brakes mayeither drag or develo dangerous slack. 4

I accomplish this end by embodying the replenisher in the compressor asan integral part thereof, the compressor mechanism being arranged topump a surplus of liquid into the system with each application of thebrakes, the excess liquid being discharged back into a reservoir. afterthe application has been completed.

Another object is the simplification of the operation of initiallyfilling the system with liquid, which I secure by a check valve readilyinsertable between the compressor and the rest of the system therebytransforming the compressor into a p p- In addition, I contemplate animproved design of compressor unit which, without material 30 changes,is adapted more or less universally for all commercial makes ofautomobiles so that the compressor unit can be standardized and incorvporated in the standard makes of automobiles without necessitatingstructural redesigning oi of the body, thereby simplifying the manufac-K 40 turers assembly problems.

A still further object is to make available to the driver some kind ofalarm indicating that the reserve supply of liquid is about exhausted,before the brakes are actually unusable, and especially before thereserve liquid has been so far depleted that it will be necessary, inreplenishing the reserve, to bleed the line to exhaust any air which mayhave been introduced. 1

The foregoing and many other objects, features and advantages of myinvention are set forth in further detail in the following descrip- Vtion which explains what I consider a preferred embodiment of myinvention. My invention,fof j course, is not inherently confined to theparticularform, system or combinations shown, but many and the brakepedal linkage;

changes may be made without departing from the spirit or scope of myinvention.

In the attached drawings to which the description refers,

Figure 1 is a plan view of a skeleton chassis, of an automobile equippedwith the improved bydraulic braking system of my invention;

Figure 2 is a verticaLelevation from the side which may be considered astaken on the line 22 of Figure 1, and shows the compressor unit Figure 3is an elevation of the inner side of the right front wheel brakeassembly taken on the line 3-3 of Figure 1, the wheel cylinder beingbroken into longitudinal section;

Figure 4 is a transverse vertical section of th same brake mechanism asFigure 3, and is taken. on the lines 4-4 of Figures 1 and.3; I Figure 5is a longitudinal vertical section through the compressor unit, whichmay be considered as taken on the line 5 5 of Figure 1;

Figure 6 is a transverse vertical section of the compressor unit takenon the somewhat irregular line 6-6 of Figure 5;

Figure 7 is a fragme ary transverse section similar to Figure 6, buttaken along the .line

' 1-4 of Figure 5 and forwardly of the sections of Figure 6;

Figure 8 is another fragmentary viewof the compressor showing thecompressor at the time the brakes are fully applied;

Figure .9 is a fragment of Figure 5 showing the check valve moved to aposition between the compressor and the rest of the system to transformthe compressor into a pump for filling the system.

Figure 10 is a view similar to Figure 5 (but looking toward the lefthandside of the automobile, rather than toward the right hand side as inFigure 5) showing a modified form of the compressor unit.

Figure 11 is a detailed section taken on the line llll of Figure 10showing the check valves of Figures 5, 8,'and 9 as applied to amodification I the piston.

In Figure 1, I have indicated an automobile chassis comprising a frameformed from side channels 10 and cross channels II, II, and",

front and rear axles i4 and I5 and front and rear wheels l6, and II. Abrake pedal pivot shaft 18 is supported'with the-aid ofa bracket. 19from the transmission'housing 2|! -(see also Flgure.2).'

The shaft l8 "pivotally supports the brake pedal 20' which though a linkrod 2| actuates a compressor unit indicated generally at C. The brakepedal is returned to normal under the influence of a light spring 2|.

A pair of conduits 22 preferably of copper or brass tubing, leadlaterally from the compressor C and connect with similar conduits 23which extend longitudinally of the chassis along or within the sidechannels III of the frame to points fifteen inches or so short of thefront and rear axles. From these points the conduits are continued withthe aid of suitable fittings as flexible but non-expansible hoses 24preferably of the type shown in patents to Malcolm Loughead No.1,457,781 and No. 1,468,601.

The outer ends of these hoses connect with cylinder blocks 25 which aresecured by bolts 26 to the steering spindles 21, in the case of thefront wheels, and to the rear axle housing in the case of the rearaxles.

Referring now to Figures 3 and 4 which show the right front wheel brakeconstruction which is typical of all of the wheel brakes, the hose 24communicates through passages 28 with the interior of the cylinder 25midway between its ends. A pair of opposed pistons 29 'are slidablymounted in the bore of the cylinder 25 and carry cup washer packings 30preferably of vulcanized rubber which abut the faces of the pistons butwhich are not attached thereto. The pressure of the fluid in the systemis relied upon to hold the packings against their pistons. In order tocut down the volume of fluid in the system, a solid cylindrical filler3| is centrally suspended be tween the proposed packings by radial pins32 and serves as an abutment to limit the inward movement of the pistons29. A molded rubber apron 33 may be slipped over each end of thecylinder 25 and also fitted over the central boss of the correspondingpiston to exclude water and dirt. v

A pivot bracket 34' stamped from sheet steel is secured by bolts 35 tothe upper side of the cylinder block 25. In the ends of thebearing slotsformed by the bracket 34 the pivot shanks 36 of the actuating levers 31are journaled. The lower ends of these levers are goose-necked aroundthe shell-like ends of the cylinder block 25 and abut the central bossesof the pistons 29. These bosses preferably carry hardened steel inserts38 for engagement by the levers 31. The upper ends of the levers 31 aregoose-necked over the brake drum 39 of the wheel l6 and are providedwith holes 40 for the passage of shanks 4| riveted to the ends of thebrake band 42. The shanks are screw-threaded to receive adjusting nuts43 against which the upper ends of the levers bear in contracting thebrake band.

The ends of the bands are normally urged apart and the levers 31 rotatedto push the pistons 29 in by means of compression springs 44-surrounding the shanks 4| and interposed between the adjusting nuts 43and a stationary stamped metal abutment 45 extending upwardly from thebracket 34. The band is anchored against rotation and adjustableradially by the usual bracket '46 supported from the mud plate 41 andpreferably lo-.

the application of'the wheel brakes, the liquid at all times completelyfllls the system and when the master compressor C is actuated by thebrake pedal 20, pressure is built up on the fluid throughout the system,which pressure serves to move the pistons 29 apart. This rocks thelevers 31 and contracts the bands upon the drums against the pressure ofthe return springs 44. As the brake pedal is released the fluid pressurein the system is lessened and the return springs return the pistons 23to their normal positions.

For a detailed understanding of the master compressor C, attention isinvited to Figure 2 and to Figures 5 to 9 inclusive. The compressor isenclosed in a box-like housing open at its bottom side and is supportedin the installation shown by cap screws 5| passing through the web ofthe rearwardly opening cross member of the chassis frame. Thissupporting cross member in the usual motor car construction is fairlyheavy, and as will be noted the compressor is mounted near itsconnection to the lateral channel ID of the frame which, especially whenre-enforced by the gusset plate 52 (Figure 1), makes an unusually firmsupport for the compressor. However, the compressor need not besupported in this particular manner and I provide another pair of bosses5| in the rearward end of the top wall of the housing 50 for thereception of the cap screws 5| when the design of the automobile chassisframe is such as to make an attachment from the upper side moredesirable. It is in fact one of the features of my improved compressorthat it can be supported in almost any desired manner by providingsimilar tapped bosses wherever required about the housing 50, and ifallof the bosses are formed in the housing, a given compressor can beinterchangeable for. many different makes of automobiles.

The closure plate 53 which forms the bottom of the housing 50 is clampedwith a fluid tight seal against the bottom edge of the housing by amunber of cap screws 54. The housing together with the bottom closureplate 53 forms a liquid reservoir and the compressor cylinder 55 ispreferably cast integrally with the plate 53 on its upper side so thatthe cylinder is mounted wholly within the housing 50. In order tominimize the possible leakage of fluid from the reservoir, I bring thecompressor actuating crank through the housing wall at the highest levelof the reservoir and above the level to which liquid can be poured intoit. This compressor actuating crank comprises a horizontally disposedshaft 56, a downwardly ex-' 6) so that the only possibleleakage of fluidwould be along the bushing 62, and such fluid leakage is furtherprevented by a packing 63. The bushing 6| abuts the inner end of thebore 6|), and together with the bushing 62serves to space the inner arm51 centraily of the housing and especially centrally in respect to thecylinder 55. Both arms of the crank are of course non-rotatably securedto the shaft 56 and one of the arms, the inner arm 51 in the drawings,is adjustable with relation to the shaft by a serration of the shaft 56and by the clamping screw 64.

The brake link rod 2| carries a screw threaded clevis on each end, theforward clevis being pivoted to the brake pedal 29v by a pin 65 and therear wheel brakes. The provision of the three holes 59 in the, crank arm58 gives a-reasonable leverage adjustment so that the foot pressure forapplying the brakes can be suited to the preferences of the individualdriver.

The compressor cylinder is open at its rearward end and in its bore apiston 61 is slidably mounted. At its forward end the piston 61 carriesan annular packing 68 which is V or U-shaped in section and preferablyformed of vulcanized rubber. It is fixed to the piston by slipping itover the enlarged head of the centrally protruding hollow boss 69 at theforward end of the piston 61.' Pressure forwardly of the piston tends toseal the packing 68 against both the boss 69 and the bore of thecylinder 55 and effectively prevents leakage past the piston even thougha very high pressure is built up on the liquid.

The cylinder 55 communicates with the conduit tubes 22 leading to thebrake cylinders by means of a vertical-passage 1| leading downwardlyfrom the forward end of the cylinder 55, a rearwardly extendinglongitudinal bore 12 and cross bores 13 in the ends of which the conduittubes 22 are secured by conventional solderless couplings.

As thus far described the compressor acts as a compressor in the strictsense of the term, that is, the piston of the cylinder serves merely todisplace the liquid and when released the return springs of the brakespush the liquid back into the compressor, there being no check valves.

However, in 'order to compensate for liquid losses in the system Iincorporate a pump as a part of my, compressor whereby an excess amountof liquid from which the system may be replenished is trapped in thesystem with each ap-' plication of the compressor.

I prefer that such a'trapping or replenishing device be combined, forthe sake of economy and simplicity, with the compressor itself and tothis end I'provide the piston 61 of the compressor with a central bore10. The rear of the bore 18 is connected with the reservoir of thehousing through a backwa'rdlyseating check valve while in the other endof the bore there is a stationary piston which also incorporates abackwardly seating check valve,thereby forming a pump. The check valveat the rear of the bore 19 is in the form of a vulcanized rubber packing14 mounted on a steam 14A fixed to aldisc 15 of hardened steel which issecured in the rear face of'the piston 61 by a 4" ring 15A. (The purposeof the hardened disc 15 is to provide a wear resisting abutment forengagement by the end of the in-' end of the arm 51, so that when, aswill belater explained, the compressor is used as a pump for filling thesystem, the piston .can be actuated positively in its rearward as wellasits forward movement.) I

The forward check valve and fixed piston for the pumpbore 10 is formedby a vulcanized packing 11 which may be identical with the packing 14and which is mounted at the rearward end of a small piston rod 18. Therod 18 also carries a perforated disc 19 to re-enforce the packing 11when the latter acts as a piston. The forward end of the piston rod 18is rather loosely held by a cross pin 19 in a plug 80 threaded into theforward end of the cylinder 55 to give the rod 9. limited universalmovement and permit the packing 11 and disc 19 to center themselves inthe bore 19' of the piston. The aperture in the end of the cylinder 55'into which the plug 80 is inserted is of sufficient diameter to permitthe withdrawal of the packing 11 so that the packing rod and plug canall be assembled and inserted as a unit into the end of the cylinder.

As previously mentioned the piston 61 of the compressor is returnedtoits normal position of Figure 5 by the-pressure of the return springs 44at the wheel brakes. 'I'he rearward movement of the piston is limited byan adjustable stop screw 8| threaded into an ear 82 protruding from .theright side wall of the housing 50, which screw engages the outer cranklever 58. In the upper wall of the cylinder 55 and just forwardly of theposition assumed by the knife edge of the packing 68 when the cylinder61 is in its normal retracted position, I provide a small relief port83. If after ,the return springs 44 in the wheel brakes have returnedthe compressor piston 61 as far as the stop screw 8| will permit, thereis still some liquid which must be displaced from the system before thereturn springs finally push the cup packings 88 of the wheel brakes asclosely together as the cylindrical fillers 3| will permit,-then thisexcess fluid will be forced out of the system through this small reliefport 83.

The relief port 83 does not cause any appreciable loss of fluid from thesystem in actuating the compressor for three reasons: First, it islocated so close to the packing 68 that as soon as there has been anyapprecialtle forward movement of the piston 61, the'port will be closedon; second, the port is so small that pump to introduce an excess amountof liquid into the. system which would readily compensate for any lossthrough the port.

The port 83 acts to relieve the system not only of the excess liquidpumped into it by the piston packing 11 but also to relieve it from anexcess volume which might develop by a general heating of the liquid inthe system as for example by driving along a hot pavement in summerweather or by driving the automobile down a longhill where the 'heatgenerated by the friction of the brakes would serve to heat-the liquidand expand it. The pump feature on the other hand havevbeen iost fromthe system. by a slight leakage, evaporation, seepage past the pistonpacking 68, or otherwise. a

As the brake pedal 29 is depressed, the arm 51 swings forwardly slidingthe piston 61 inwardly. Almost instantaneously the port 83 is shut ofi'and the pressure built up in the system serves toseal the packing 68against the bore of the cylinder 55 and also against the central boss 89of the piston 61 while the pressure on the packing 14 seals it againstthe bore 10 of the piston. In effect, the entire area of the piston 81within its perimeter becomes the piston face in displacing liquid fromthe cylinder toward the wheel brakes. The liquid displaced from the bore18 by the packing I4 slips past the piston packing 11. A normal fullapplication of the brakes would carry the piston forwardly approximatelyto the position indicated as a typical example in Figure 8. In theparticular apparatus which I have illustrated in the drawings, the fluidsystem '(not including the reserve of course,) contains about twenty-onecubic inches of liquid and in the normal maximum application of thebrakes, the compressor displaces about 1.25-cubic inches of liquid. Itwill be; seen from Figure 8 that the piston is then still capable of amovement a half more than the normal movement, thereby giving a fiftyper cent margin of safety in the event that the brake linings becomeworn down, the linkage develops slack, or the reserve of liquid becomesdepleted-and no other adjustment is made to compensate for it. Theamount of excess liquid introduced by the displacement of liquid fromthe bore 18 of the piston would be about .196 cubic inches or a littleless than one-sixth of the normal displacement.

the pressure forwardly of the piston packing l1 1 is greater than thatin the bore 10. This seals the edges of the packing against the bore inwhich it is sliding. The fluid from the reserve in the housing 58 willflow into the bore I8 past the check valve packing 14, partly by suctioncreated in the bore 18 and partly by the head of liquid in the reserve.When the piston 81 has receded to its normal position, the bore 18 willhave been completely charged with liquid.

' If one considers the packing 88, the boss 55 This necessitatesinterposing a check valve somewhere between the compressor cylinder 55and the conduit lines. Instead of using valves-with their attendantdanger of leakage-to by-pass the communicating passages between thecylinder and the lines through a conventional check valve, I havedevised a construction which is virtually built into the compressor unit'as an integral part and which avoids possibility of leakage. Thisconsists of a cap screw 88 threaded into the bottom closure plate 53 ofthe compressor unit in alignment with the bore I2, the cap screw 88having a reduced extension 89 carrying an integral perforated disc 98which has a tight fit in the bore 12. On the extreme end of theextension 89 a disc valve 9| is loosely mounted and can seat as a flapvalve against the disc portion 98 to close communication through itsperforations.

As normally supported by the plug 88, the disc 98 and valve 8| arepositioned at the extreme rearward or closed end of the bore 12 andbeyond the intersection of the bore 12 by the cross bores 13, so thatthe check valve 90-!!! does not affect free communication between thecylinder 55 and the conduit lines. When the compressor is to be used asa pump for filling the system, however,

inder 55 and the conduit lines. In this positionv the check valve seatstoward the cylinder 55 preventing recession of the liquid from the linesand and the packing '14 asv constituting the face of the piston 81,which they do in effect, it will be seen that the packing I1 acts as acheck valve to trap a portion of the liquid displaced by the piston andprevent its return to the space from which it was displaced and insteadleave it to to be discharged through the relief port 88.

When the apparatus is originally assembled and the system is to be madeready for operation, the filling plug 85 is removed from the top wall ofthe housing 58 and liquid is poured in to fill the housing. The reliefvalves 88 at the wheel brakes are opened. One of these valves 88 asshown in pistons. The valve is in the form of a plug which seats againsta counter-bore in the cylinder block 25' and which has a small bore 81leading from its outer end to a cross bore adjacent its inner end. Thewheel cylinder is thus relieved to at-. mosphere by simply turning ,backthe valve 88 a short distance from its seat. The relief valves arelocated at the tops of the wheel cylinder blocks 25 because they are thehighest points at the extremities of the system.

It would be possible, if the pump portion of the compressor piston 61were properly primed and if the brake pedal 28 was reciprocated fastenough,

to pump the reserve fluid into the system and completely fill it. .Butin order to simplify this operation and make, it more positive I preferto transform the entire compressor into a pump.

causing the cylinder 55 to be filled at each stroke partly through therelief port 83 and partly past the packings TI and 14 and to a lesserextent past the packing 8. A suitable vent is provided for the housing5v either through the filling plug 85, or preferably, as shown in Figure5, by a small hole 92 in the vertical wall of the housing extension thatprovides room for the top of the arm 51, as that is well above thehighest liquid level and where there is little danger of dirt beingintroduced.

As soon as the system becomes entirely filled, the liquid will startrunning out the relief valves 88 at the wheel brakes and then theoperator cancease actuating the compressor, turn the screw 88 back toits normal position and close the relief valves 86.

Very minor liquid losses are almost sure to occur from time to timeeither due to slight leakage past the pistons of the wheel brakes or inthe couplings, or to evaporation or the like, with the result that atthe end of a year or two, the liquid reserve in the housing 50 will havebeen brought down ,to a level lower than the relief port. I contemplatethat this will not happen in the majority of instances because theautomobile driver will take the precaution of checking up on i theliquid level at long intervals. Although the exposure of the port 88 toatmosphere might tend toadmit some air into the cylinder 55, the effectwould be overcome by the action of the pump portion of the compressorwhich, in delivering its excess liquid to the cylinder 55, would drivethe air through the port along with the excess liquid. When the liquidlevel has dropped down to the perforations 153 in thedisc l5 and thetroducing a portion or air with each application of the compressor,increasing as the liquid level falls. Even though this air will berelieved from the cylinder 55 by the relief port 83 at the completion ofeach stroke, the air during the stroke will be trapped in the cylinder55 with the result that it acts somewhat as an expansion chamber to givea certain compressibility to the fluid in the system. This conditionwill be indicated to the operator by a springiness" of the brake Thisslack in the application of the brakes due to exhaustion of the reserveliquid, of course, does not develop suddenly but over a considerableperiod 01 time so that the brakes are still usable and the driver isgiven ample time in which to attend to replenishing the liquid.

As to the relation between the capacity of the ump and that of thecompressor, the pump should be of suflicient capacity to compensate forminor fluid losses from the system, but still it should not be of suchcapacity that it. will cause all of the slack to be taken up by pump ingan excess of fluid into the system should the' driver successively applyfull and then relaxed pressures by the compressor without letting thecompressor pistoncome back to normal where the cylinder will be drainedof excess fluid by the port 83. Thus, as here shown, the pump could beactuated two or three times or more without an intervening relief,without pumping so much liquid into the system as to take up the slackon the brakes and cause them to lock.

' It will be observed that if the piston 61 were an ordinary pistonthatis did not have the pump formed by the bore IO-its effective areainmoving inwardly would be slightly more than in a moving outwardlybecause of negligible slippage past the cup washer 68, However this isonly incidental as compared with the diflerential between the effectiveareas of the piston when moving forwardly and moving backwardly, when mycentral pump is incorporated in it.

In the modifled i'orm oi' compressor unit shown in Figures 10,11, and 12the cylinder 550: forms a part of 'a more or less circularend plate 53arather than a part ofthe bottom plate, so that I the cylinder isinserted from the end of. the main housing 50.

, Instead of using the retractile spring 2] for the brake, pedalpositively towithdraw the piston through the coupling aflorded'by thepin 16,- I

use a retractile spring 95 interposed between the piston and thecylinder. This permits the brake pedal to return to normal independentlyof the piston and tends at all timesto keep the piston cup 68a againstthe piston.

' I provide a stop for limiting the outward movement or the piston, inthe form ora spring wire .86. The wire is bent into a C-shape ofsomewhat more than 180 degrees so that it will securely grasp thecylindrical periphery of the end 01 the cylinder. It has hair pin-rehentends 91, with the terminals oflset'inwardly as at 98 on a diam eter. Theoffset ends extend through holes ill in the wall of the cylinder 55!;and project a short distance inwardly therebeyond as a stop for thepiston 61a. jI'he purpose of therelatively great developed length is tominimize the danger oi the spring wire being bent beyond its elasticlimit in removing it.

A discharge passage I00 leads'irom the inner end of the bore of thecylinder 55a down past the normally inoperative check valve 890. and tothe line 22a leading to the wheel brakes.

I claim 1. In a hydraulic brake system of the-class de- -scribed havingbrake mechanisms operated in one direction by fluid pressure and springsfor opercompressor, and valve means for draining the system of excessliquid when the compressor is in its position of rest.

2. In a fluid pressure system of the class described dncluding a fluidmotor and means oper-' ated thereby, the combination or a compressor influid communication with said motor, said compressor having areciprocating piston, said piston having one area effective on thedischarge stroke and a second area effective on the return stroke, saidfirst-mentioned area being greater than said last-mentioned area wherebysaid piston on its forward stroke discharges from said compressor alarger quantity of fluid than can be accommodated in said compressor bythe return stroke of said piston, and means for conducting saiddifference in quantity of said fluid to a. fluid reservoir.

3. In a hydraulic brake system having brakes hydraulically actuated inone direction and spring means for returning said brakes to inoperativecondition, the combination of a compressor comprising a cylinder elementand a piston element, a. liquid connection between the compressor andthe hydraulically actuated brakes, a pump coaxiaily arranged with thecompressor and comprising a cylinder element and a piston element, oneof said pump elements being carried byone of said compressor elements,and a common actuating member for the compressor and the pump compressorcylinder and for pumping the surcharge of liquid from the pump cylinderinto the compressor cylinder, a fluid reservoir, andmeans for conductingto said reservoir the .excess of the surcharge returned through theoperation of said springs. r

4. In a hydraulic braking system of the class described havinghydraulically actuated wheel '65 brakes and springs iorreleasing saidbrakes and for returning fluid supplied thereto, the combination of acompressor in liquid communication with i said wheel brakes, saidcompressor comprising a cylinder, a compressor piston reciprocabletherein, said piston having a bore, a pump piston actingin said bore andincluding a check valve permitting the liquid to pass from. the boreforwardly into the cylinder, a liquid reservoir for supplying i iiluiclvtosaid compressor and bore, a check valve }carried by the compressorpiston permitting the for simultaneously compressing the liquid in the5. In a hydraulic pressure system of the class described having meansoperated in one direction by hydraulic pressure and returned by springmeans, the combination of a compressor in liquid communication with saidhydraulically operated means, said compressor comprising a liquidreservoir, a master cylinder submerged therein, a compressor pistonreciprocable in said cylinder, said piston having a bore constitutingthe cylinder bore of a pump, a pump piston .working in the pump bore andincluding a cup packing having a check valve action permitting the flowof liquid from the pump bore to the cylinder, a check valve between thepump bore and the reservoir located outwardly from said pump piston,means for actuating .the compressor piston to operate the compressor andthe pump, means for returning the compressor piston independently of anyback. pressure created by said springs, and passage means between thecompressor cylinder and reservoir for relieving excess liquid returnedto saidcylinder under the influence of said spring means. 6. A mastercylinder unit for a hydraulic brake system having brake mechanismoperated in one direction by hydraulic pressure and in the oppositedirection by spring means comprising a compressor cylinder, a pistontherein, a reservoir communicating with the outer end of the piston,means for reciprocating the piston for compressing the liquid in thecylinder, and a reciprocating pump formed within the piston and actuatedby the reciprocation of the piston for pumping a surcharge of liquidfrom the reservoir into the cylinder, and means for returning tothereservoir excess liquid returned under the influence of said springmeans.

1 '7. In' a hydraulic brake system comprising means and said pumpmeans,said reciprocable 8. In a hydraulic braking system having liquidoperated wheel brakes, the combination of an actuating compressor inliquid communication with said brakes, and normally inoperative meansmanually manipulable to operable condition as a discharge check valvefor the compressor to prevent recession of liquid from the brakes to thecompressor whereby the compressor may be actuated as a pump to fill theliquid system therebeyond.

9. In a hydraulic braking system including liquid operated wheel brakes,the combination of an actuating compressor having liquid inlet meansfrom a source of liquid supply, there being operating liquid connectionsbetween said compressor and said wheel brakes and normally in operativemeans manually rendered operable as a discharge check valve for thecompressor to prevent recession of liquid from the brakes to thecompressor whereby the compressor may be actuated as a pump to fill theliquid system.

10. In a hydraulic braking system having liquid operated wheel brakes,the combination of an actuating compressor having liquid inlet meansfrom a source of liquid supply, there being operating liquid connectionsbetween the compressor and the wheel brakes, and a discharge check valvefor the compressor'preventing recession of liquid from the brakes to thecompressor whereby the compressor may be actuated as a pump to flll theliquid system, and means operable at will'to render the check valveinoperative.

11. In a hydraulic braking system having liquid operated wheel brakes,the combination of an actuating compressor having a passage in liquidcommunication with said brakes, and a check Naive manually shiftableinto'and out of said passage whereby in the latter position the checkvalve becomes inoperative and in the former position operates to preventrecession of liquid from the brakes to the compressor when thecompressor is actuated as a pump.

12. In a hydraulic system-oi the. class described having elementsactuated by hydraulic. pressure, the combination of a compressor havingan operating liquid connection with said elements, check valve means inthe connections through which'liquid passes to and from the compressor,and manually operable means to adjust the check valve means to permitliquid flow in either one direction only or in both directions.

13. In a hydraulic pressure system of the class described,includinghydraulically actuated mechanism, the combination of a compressor,liquid lines leading from the compressor to said means, a liquid passagebetween the compressor and the lines comprising intersecting bores, acheck valve in one 01 said bores comprising a stem, a perforate headmaking a substantially fluidtight fit with the check valve bore, a checkvalve element cooperating with the perforate head, and manual means forreciprocating the check valve in its bore across the intersection ofsaid bores whereby in one position the check valve is operably insertedin the passage and in the other position it is rendered inoperative.

WALLACE F. onrvna.

